The present invention broadly relates to diesel engines equipped with exhaust gas particulate filters, and deals more particularly with a method for reducing exhaust smoke emissions following a period of extended engine idling or low load operation.
Emission after-treatment devices are used to collect particulate matter from the exhaust gas of internal combustion engines. In particular, conventional emission treatment devices for diesel engines include particulate filters, oxidation catalysts and nitrous oxide (NOx) catalysts. A problem exists with particulate filters in that the particulates, which consist largely of carbon particles, tend to plug the filters, resulting in a restriction to the flow of exhaust gas. In order to periodically regenerate or purge the filter from particulates, it is known to take measures which result in an increase of the exhaust gas temperature above a predetermined level (e.g. above 450xc2x0 C.) in order to incinerate the carbon particles accumulated in the filter.
One conventional method used to increase the exhaust gas temperature involves controlling a throttle valve in the intake manifold of the engine. In particular, it is known that by throttling/closing the throttle valve, the exhaust gas temperature may be increased. Numerous methods have been used for controlling the throttle valve. For example, in one conventional method, the intake throttle valve is controlled by utilizing the difference between a calculated target intake manifold pressure, and an actual intake manifold pressure. The target intake manifold pressure is calculated using an engine speed and engine load. Normally, regeneration of the particulate filter through an increase in the exhaust gas temperature is accomplished during light engine load operation. The regeneration process is scheduled by engine control software based on an estimate of the particulate loading.
When a diesel engine remains at idle speed or low load operation for an extended length of time, gaseous hydrocarbons as well as water accumulate in the particulate filter, primarily because the exhaust gas temperature falls to a relatively low level that is inadequate to evaporate the accumulation. A large accumulation of gaseous hydrocarbons and water results in the production of blue or white smoke in the exhaust gas when the engine is accelerated above idle speed with resulting higher exhaust temperature. This production of exhaust smoke is highly undesirable
Thus, there is a clear need for a method for reducing exhaust smoke emissions following extended diesel engine idling or low load operation.
The present invention provides a method of reducing smoke emissions in diesel engine exhaust following a period of extended diesel engine idling or low load operation.
According to one aspect of the invention, a method is provided for periodically purging a diesel particulate filter used to capture diesel particulates in the exhaust of a diesel engine, comprising the steps of sensing when the engine is operating at a speed corresponding to an idle condition or low load; determining when the engine has remained at the idle speed or low load condition for a predetermined length of time; and, increasing the temperature of the exhaust gas entering the filter to a preselected temperature sufficient to purge the filter, but only after it has been determined that the engine has been idling or at low load for a predetermined time period.
The method is preferably carried out by storing a count corresponding to the length of time that the exhaust gas temperature is less than a predetermined temperature below which gaseous hydrocarbons and water accumulate in the filter. A timer for storing the time count is incremented while the engine remains at idle speed or low load, and is decremented when the exhaust temperature rises above a second threshold value at which purging of the filter. When the time count exceeds a preselected value corresponding to a condition well before the filter has accumulated an amount of hydrocarbons and water that could result in smoke emissions, a purging event is initiated in order to oxidize the gaseous hydrocarbons and evaporate the water, thereby reduce the possibility of smoke emissions from the engine""s exhaust.
According to another aspect of the invention, a method of reducing smoke emissions in the exhaust of a diesel engine equipped with a diesel particulate exhaust filter is provided, which comprises the steps of sensing the temperature of the exhaust gas entering the filter; starting a time count when the sensed exhaust temperature is below a preselected value and the engine is operating at a speed corresponding to an idle or low load condition; purging the filter by increasing the temperature of the exhaust gas; sensing the temperature of the exhaust gas exiting the filter; and, resetting the time count when the sensed temperature of the exhaust gas exiting the filter exceeds a second, preselected value greater than the first value.
Accordingly, it is a primary object of the present invention to provide a method of controlling a diesel engine which reduces smoke emissions in the exhaust gas.
Another object of the invention is to provide a method as described above which reduces the accumulation of gaseous hydrocarbons and water in a diesel exhaust particulate filter during extended engine idling or low load operation.
These, and further objects and advantages of the invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.